pw_tokenizer: Make pw_span dep public since it is used in a header
pw_tokenizer: Make pw_span dep public since it is used in a header

Change-Id: I9120ddeb0fe8903740ccfba0e4c90614c45ffdbc
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/100460
Pigweed-Auto-Submit: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Reviewed-by: Armando Montanez <97ef6fdb231c129ac8827d9f0c4106bfbf57f74f@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed